Physics and Astronomy

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Open Access
Double-Loop Microtrap Array for Ultracold Atoms
(2015-01-26) Jian, Bin; Van Wijngaarden, William A.
A novel kind of magnetic microtrap is demonstrated for ultracold neutral atoms. It consists of two concentric loops of radii $r_1$ and $r_2$ having oppositely oriented currents. A magnetic field minimum is generated in three dimensions that can be used to trap the atoms with a trap depth of about 1 mK using a current of 2.6 A. The condition $r_2/r_1$ = 2.2 maximizes the restoring force on the atoms toward the trap center. Unlike conventional magnetic microtraps, an external bias field is not required. Moreover, a one dimensional array of double-loop microtraps can be created by daisy chaining single microtrap circuits. A linear array of three microtraps having $r_1$ = 300 $\mu$m was fabricated as part of an atom chip. The following three techniques were developed to load the microtrap array: 1) atoms initially contained in a magneto-optical trap (MOT) were transported to the atom chip by a conventional magnetic trap, 2) atoms were first loaded into a mirror MOT and 3) atoms were initially loaded in a far off resonance optical dipole trap (FORT). Each technique loaded greater than $10^5$ $^{87}$Rb atoms into the microtrap array. The lowest temperature of 30 $\mu$K for the microtrapped atom cloud was achieved using FORT loading. The strength and the position of the microtrap could be precisely adjusted over a range from 300 to 50 $\mu$m above the atom chip surface by applying an external bias magnetic field. The lifetime of the atoms trapped in the microtrap array was measured to be 350 ms which was limited by the collisions with residual background gas.
Open Access
Topological Dynamical Systems Methods in Early-Universe Cosmologies
(2015-01-26) Kohli, Ikjyot Singh; Haslam, Michael C.
This dissertation describes some important problems that we have tried to solve with respect to the state of the early universe, that is, the universe shortly after the Big Bang. Standard early-universe cosmological approaches almost always assume a perfect-fluid isotropic and spatially homogeneous Friedmann-Lemaˆıtre- Robertson-Walker (FLRW) model to study the universe’s evolution. The problem is that the early universe was in a hot, dense, and unstable state. Hence, perfect-fluid models which assume no dissipation may not be accurate at such early epochs in the universe’s evolution. Our approach is to introduce terms in the Einstein field equations that allow the representation of these dissipative/viscous effects. In addition, we relax the condition of isotropy to obtain a class of anisotropic and spatially homogeneous cosmological models, known as the Bianchi models. Our research then is largely focused on studying the dynamics of these Bianchi models in the presence of viscous effects. We feel that studying the early universe in this context is more fruitful than the standard approaches mainly because our models are more realistic representations of the conditions of the early universe. Our technique for studying these models is also quite different than the standard approaches in the literature, in that, we use topological dynamical systems theory to study the early and late-time asymptotic behaviour of the cosmological model under consideration. Our work in this regard has been quite successful, and has led to a number of publications in the Physical Review which are listed in the main dissertation document.
Open Access
Ionization of the Hydrogen Molecular Ion by Strong Infrared Laser Fields
(2015-01-26) Tsednee, Tsogbayar; Horbatsch, Marko
The ionization of simple molecular targets, such as molecular hydrogen, or even the molecular hydrogen ion ($\mbox{H}^{+}_{2}$) by strong laser fields has become the focus of experimental research in the past few decades. On the theoretical side the problem presents two challenges: on the one hand one has to solve the problem numerically even in the one-electron case ($\mbox{H}^{+}_{2}$), since no analytic closed-form solution is possible; on the other hand there is the many-electron problem ($\mbox{H}_{2}$ and other diatomic molecules, such as $\mbox{N}_{2}$, $\mbox{O}_{2}$, etc.), which currently is at the limit of computational feasibility ($\mbox{H}_{2}$), or exceeds it for molecules with more than two electrons. In this thesis the single-electron problem of the hydrogen molecular ion in intense continuous-wave laser fields is addressed. The focus is on ionization rates of the molecule as a function of internuclear separation within the framework that the motion of the nuclei can be neglected (Born-Oppenheimer approximation). First, the problem of the DC limit is considered, i.e., a strong static electric field is applied along the internuclear axis. The field ionization rate is calculated by solving a stationary non-hermitean Schr\"odinger equation in a suitable coordinate system (prolate spheroidal coordinates). Some previously obtained values from the literature are reproduced; for larger internuclear separations improved values are obtained. For the more interesting case of an infrared (continuous-wave) laser field Floquet theory is applied to transform the time-dependent Schr\"odinger equation for the electronic motion into a non-hermitean coupled-channel stationary problem. Ionization rates are found as a function of laser frequency ($\omega$), and the low-frequency limit is pursued to understand how one can establish a connection to the DC limit. Results are obtained for the two lowest electronic states, which are named the {\it gerade} and {\it ungerade} (or even and odd) ground states in the field-free limit. From the calculated results it is observed that the ionization rates peak at certain internuclear separations, such that a dissociating $\mbox{H}^{+}_{2}$ molecule will be preferentially field ionized. In addition, the thesis reports on calculations of so-called high harmonic generation - a process where photo-electrons acquire energy from the laser field, are deflected back by the linearly polarized laser and recombine under the emission of photons with energies that correspond to odd-integer multiples of the laser photon energy.
Open Access
ATRAP Buffer-Gas Positron Accumulator
(2015-08-28) Comeau, Daniel Andre; Hessels, Eric
The ATRAP collaboration has been creating antihydrogen, the simplest antimatter atom, since 2002 and has a long-term goal of performing precision laser spectroscopy on these antihydrogen atoms. ATRAP has produced antihydrogen by positron cooling of antiprotons and by a laser-controlled charge-exchange process. Both methods require large numbers of antiprotons and positrons (the constituent particles of antihydrogen). This dissertation describes the methods developed to increase the number of positrons available for the ATRAP experiments by a factor of 200. The development of the new positron loading scheme has enabled the ATRAP collaboration to greatly increase the daily rate of antihydrogen production. Positrons originating from a radioactive source travel through a moderating material and are accumulated in a differentially pumped vacuum chamber. When required, the positrons are sent through a complex magnetically-guided beamline to the location where antihydrogen is produced. The system built allows for a reliable, highly-efficient method of providing positrons to the ATRAP experiment.
Open Access
Electron Removal Processes in Proton-Methane Collisions
(2015-08-28) Salehzadeh, Arash; Kirchner, Tom K. R.
We have conducted a quantum-mechanical analysis within the independent elec- tron model to investigate electron removal processes in the proton-methane collision system in the 20 keV to a few MeV energy range. Similar to a previous work, we have used a spectral representation of the molecular Hamiltonian and a single-centre expansion of the initially populated molecular orbitals. The two-centre basis gen- erator method is then used to solve the time-dependent single-particle Schr ̈odinger equations. We have also used the “independent atom model” in which we have treated the collision system with a molecular target as a combination of collision systems with atomic targets. We have also shown that Bragg’s additivity rule is derived from the independent atom model. The results for net capture and ionization cross sections, obtained by the molec- ular method as well as Bragg’s additivity rule, are compared with available ex- perimental studies. We observe good agreement at high energies for both models. At intermediate and lower energies the situation seems to be less clear. For the molecular method the ionization results are improved when we estimate excitation particularly at intermediate energies. Overall, our molecular method outperforms Bragg’s additivity rule for both capture and ionization.
Open Access
Photometric Calibrations of Metallicity and Temperature For M Dwarfs
(2015-08-28) Hejazi, Neda; Robertis, Michael De
Based on a carefully collected sample of dwarf stars, a new empirical photometric calibration to estimate the metallicity of late-type K and early-to-mid-type M dwarfs is presented. The calibration sample has two parts; the first part includes 21 M dwarfs in common proper motion pairs with an FGK star or early-type M dwarf of known metallicity and the second part contains 50 dwarfs with metallicities obtained through moderate-resolution spectra. Using the most recent BT-Settl model atmospheres and the estimated effective temperatures of stars in the calibration sample, the synthetic colour-colour diagram most sensitive to M-dwarf temperatures is identified. By applying these methods to a large sample of around 1,300,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) and the Two-Micron All Sky Survey (2MASS), the metallicity and temperature distributions of these small stars are determined. Using a photometric parallax, the Galactic heights of stars in the large sample are calculated. Our results show a shift in metallicity distribution toward lower metallicities as a function of Galactic height. The relation between metallicity and absolute magnitude is also investigated. A scarcity of metal-poor dwarf stars in the metallicity distribution relative to the Simple Closed Box Model indicates the existence of the “M dwarf problem,” similar to the previously known G and K dwarf problems. It is shown that the Galactic chemical evolution models proposed to solve the G and K dwarf problems could also be a solution of the M dwarf problem as well.
Open Access
Differential Absorption Lidar Measurements of Troposheric Ozone in the Arctic
(2015-08-28) Seabrook, Jeff Adams; Whiteway, James A.
A differential absorption lidar was constructed at the laboratory at York University and deployed in field campaigns to measure vertical profiles of tropospheric ozone. Profiles of ozone concentration were derived from the range-resolved simultaneous detection of backscatter from two or more wavelengths of laser radiation. By analyzing the absorption differences due to ozone between the two lidar returns, an ozone profile along the optical path of the laser was determined. This method is capable of resolving ozone concentrations between a range of 300 m to 8 km from the lidar. During the spring in the polar region, tropospheric ozone depletion events occur due to the presence of inert halide salt ions such as Br- in the atmosphere. After polar sunrise, this Bromine photochemistry can cause ozone concentrations near the ice surface to drop to near zero levels. Outstanding questions addressed by the lidar measurements were (a) whether significant ozone depletion occurs in layers not connected to the surface, and, (b) how local topography can influence ozone concentrations measured at land based locations such as Eureka NU. Measurements were made during three field campaigns. The first was on the Amundsen icebreaker ship of the Canadian Coast Guard as part of the circumpolar Flow Lead study. For the second campaign the lidar was installed on the Polar-5 aircraft for flights over the sea ice north of Barrow Alaska. The third campaign involved ground based measurements from Eureka Weather Station on Ellesmere Island in the Canadian High Arctic. All of the measured ozone depletions were connected to the surface, and no evidence of ozone depleted air detached from the boundary layer was found. The lack of free tropospheric depletions indicate that such events are likely rare, and not a significant ozone sink. While measuring tropospheric ozone from a land based location, the measured depletions were found to be mainly confined to the atmospheric boundary layer except in instances where surrounding topography enabled the transport of ozone depleted air into the free troposphere. This effect was common at the Eureka weather station on Ellesmere Island, which is surrounded by a number of mountain ranges.
Open Access
Cosmic Bubble Collisions: Observable Signature of a Classical Transition
(2015-08-28) Lin, Wei; Johnson, Matthew C.
The theory of inflation was introduced to resolve many existing observational problems in cosmology. Inflation becomes eternal when a region of space continuously spawns non-inflation regions. This process arises from metastable vacua in a potential landscape. Our universe could be a realization of one of these many vacua predicted by the theory. In this thesis, we explored the idea that a universe can be born via a collision between two bubble universes. This process is known as a ``Classical Transition''. In this thesis, the potential observability of relics produced during the collision is studied. If a classical transition did happen in the past, its presence is imprinted on the CMB temperature anisotropy.
Open Access
A Search For Warm-Hot Intergalactic Matter in the Local Sheet of Galaxies
(2015-12-16) Deneault, Ryan Scott; McCall, Marshall
30-40% of all baryons in the Universe are thought to reside in the warm-hot intergalactic medium (WHIM) at temperatures in the range of 10^5-10^7 K. If the oxygen abundance is comparable to expectations, then OVI absorption from the WHIM associated with the Local Sheet of galaxies should have been detected in background sources observed by the Far-Ultraviolet Spectroscopic Explorer (FUSE). FUSE spectra of targets spanning the entire sky have been examined to distinguish the WHIM in the Sheet from other sources. These observations suggest that the Sun is offset from the plane of the Local Sheet WHIM, defining a theoretical framework against which the data was compared. By looking for a correlation of the OVI absorption equivalent widths with latitude and comparing the results to hydrodynamical simulations, strong constraints have been placed on the properties of the WHIM. With a hydrogen number density equal to that predicted by the simulations, the upper limit to the oxygen abundance for the WHIM in the Local Sheet must be 0.05 ± 0.01 Z⊙. If instead a metallicity of 0.1 Z⊙ is adopted for the WHIM, the upper limit to the hydrogen number density must be 0.64 ± 0.02 times that predicted by the simulations.
Open Access
Testing CPT And Antigravity With Trapped Antihydrogen At ALPHA
(2016-09-20) Capra, Andrea; Menary, Scott Robert
High precision antihydrogen experiments allow tests of fundamental theoretical descriptions of nature. These experiments are performed with the ALPHA apparatus, where ultra-low energy antihydrogen is produced and confined in a magnetic trap. Antihydrogen spectroscopy is of primary interest for precision tests of CPT invariance - one of the most important symmetries of the Standard Model. In particular, the 1S-2S transition frequency in hydrogen is the most precisely known quantity in Physics thus measuring the same quantity with antihydrogen provides the most stringent comparison between matter and antimatter. Antimatter gravity is an open experimental question that deserves to be directly addressed in order to test the foundation of the General Theory of Relativity. Methods to produce, trap, detect and identify antihydrogen are presented in this work, alongside the first high precision measurement of an antihydrogen property, i.e., the electric neutrality of an antiatom. This measurement also constitutes a three-fold improvement to the measured value of the positron charge. The focus is then shifted to the proposed experiment to measure the antihydrogen gravitational acceleration, with particular attention to the antihydrogen detector.
Open Access
Synthesis, Characterization and Application of Barium Titanate Particles in Light Emitting Devices
(2016-09-20) Dumont, Antoine; Morin, Sylvie
The search for low-cost technologies that reduces our energy consumption is a priority in our struggle for the well-being of our environment. This project had two objectives : (1) Synthesizing BaTiO3 nanoparticles of a controlled size and structure for an electroluminescent device (ELD) (2) Analyzing the effect of doping barium titanate with lanthanum and optimizing the concentration for our application. The BaTiO3 particles created for this project will enable a more efficient use of the necessary electric energy for the emission of light in ELDs. They can also reduce the thickness of the overall device, which would result in lower production costs and increased brightness. The BaTiO3 was synthesized using a sol-gel method, which allows for the control of particle size and dopant concentration in 6 different powders. The material was characterized using scanning electron microscopy, X-ray diffraction analysis and X-Ray photoelectron spectroscopy (XPS). The XPS results showed a large split in the lanthanum's binding energy which was never discussed in the litterature. Following this, a hypothesis was advanced related to the interaction between the Ti-O strong bond and the lanthanum. The ELDs were screen-printed by hand using inks made from the experimental BaTiO3 and a ZnS commercial powder. The optimal concentration of dopant (0,5 mol% La) was obtained by using impedancte spectroscopy and photometry to determine, respectively, the electric permittivity of the BaTiO3 layer and the luminescence of the ELDs. One of the luminescent samples was found to be 600% brighter than the others. Although an anomaly among the samples, it is a real result and could reveal to be of great importance for the field of ELD research if it can be reproduced using a commercial printer.
Open Access
Higgs and Heavy Meson Lattice Spectroscopy
(2016-09-20) Wurtz, Mark Bryan; Lewis, Randy
Lattice simulations are a first principles method of numerically studying the spectrum of bound states. In quantum chromodynamics (QCD), lattice simulations have had tremendous success in accurately calculating the hadron spectrum. They also provide a non-perturbative description of the Higgs mechanism, where spontaneously broken gauge symmetry is substituted by Higgs-confinement complementarity. Presented are studies of two different sectors of the standard model of particle physics using the latest methods in lattice spectroscopy. A search for exotic states in the SU(2)-Higgs model is performed using a variational analysis. All parameters are tuned to match their experimental values, including the recently discovered Higgs mass. A vast spectrum of multi-particle states is found and all are consistent with weakly interacting Higgs and W bosons, with no exotic candidates. In the QCD sector, the spectrum of heavy mesons that contain at least one bottom quark is extracted using free-form smearing. A new "minimal-path" implementation is introduced which maintains the usefulness of the original free-form smearing method and reduces its computational time dramatically. First lattice results of assorted radially and orbitally excited bottomonium and bottom-charm meson masses are presented. Calculations of the bottom-strange and bottom-up/down mesons are also performed. The methodology and results presented within are a significant contribution to the field of lattice spectroscopy.
Open Access
Stand-Off Detection of Organic Compounds on Mars Using Ultraviolet Raman Spectroscopy and Time-Resolved Laser-Induced Fluorescence
(2016-09-20) Eshelman, Evan James; Daly, Michael
Recent discoveries of organic carbon and methane on Mars have continued to motivate the search for complex organics on the Martian surface. Instrumentation that directly identifies and characterizes organic carbon is a high priority for the Mars 2020 rover, the successor to the Curiosity rover. Although no Raman instrument has been used in a planetary setting other than Earth, Mars 2020 will contain both SHERLOC, a 248 nm Raman instrument, and a 532 nm Raman system as part of the SuperCam instrument. A 266 nm Raman spectrometer incorporating time-resolved fluorescence capabilities was developed at York University in order to investigate the performance of an ultraviolet Raman system in detecting organic material on Mars. A range of pure organic compounds, mineral-organic mixtures, and complex Mars analogue rocks from extreme environments on Earth were selected for study. This diverse sample suite allowed investigations that established the detection capabilities of the instrument using controlled samples, and demonstrated the potential for 2D mapping across rough unprepared surfaces to detect traces of organics embedded in a complex mineral matrix. While visible excitation wavelengths suffer from interfering fluorescence that can overwhelm the Raman signal, 266 nm was found to reduce or remove fluorescence in the Raman window in all samples that were tested, increasing the sensitivity to organic carbon. Many organic compounds exhibit strong fluorescence outside the Raman window when excited with 266 nm radiation. This fluorescence was investigated to determine if it could improve the ability to detect organic material. A method was developed for measuring fluorescence lifetimes with sub-ns precision, and the fluorescence decay profiles of a wide range of aromatic organic molecules were characterized. Incorporating time-domain capabilities improved both the ability to discriminate between organic compounds and the ability to separate organic from mineral fluorescence. The capabilities investigated in this work may be useful when interpreting the measurements that will be returned from the Mars 2020 mission, and for developing the next generation of flight instruments.
Open Access
Search For Magnetic Monopoles in 8 TEV Centre-of-Mass Energy Proton-Proton Collisions With the Atlas Detector at the LHC
(2016-09-20) Palacino Caviedes, Gabriel David; Taylor, Wendy J.
Symmetry is fundamental to our understanding of the laws of nature. The simplicity that is found in the symmetries that explain the most fundamental interactions is remarkably beautiful. Physicists have worked hard and continue to work even harder to deepen the understanding of nature with the hope of revealing higher symmetries, among them the symmetry between electricity and magnetism, but one piece is still missing from this puzzle: the elusive magnetic monopole. This dissertation presents a search for magnetic monopoles produced at the Large Hadron Collider in 8 TeV centre-of-mass energy proton-proton collisions using the ATLAS detector. The highly ionizing nature of monopoles was exploited to look for regions of high ionization density in the Transition Radiation Tracker and energy deposits in the Liquid-Argon electromagnetic calorimeter with very low lateral dispersion. The search used 7 fb1 of data collected by a dedicated trigger for highly ionizing particles, which made the ATLAS detector sensitive to monopoles with charge greater than the Dirac charge, in particular, twice the Dirac charge, for the first time. The results of the search were interpreted for models of pair production of spin-0 and spin-1/2 monopoles through the Drell-Yan process. A model-independent interpretation of the search is also presented. In the absence of an observation of events that were consistent with the expected monopole signal, upper limits on production cross section were set for all the scenarios considered. A model-independent limit of 0.5 fb was set for monopoles in fiducial regions of high selection efficiency. Lower mass limits were obtained for pair-produced spin-0 and spin-1/2 monopoles. This search excluded pair-produced spin-1/2 monopoles with the Dirac charge with mass below 1340 GeV, the most stringent mass limit to date.
Open Access
Semi-Empirical Modeling of Radiolytic Production in the Mars Northern Polar Region
(2016-09-20) Feng, Keh-Harng; McElroy, C. Thomas
A model to simulate the radiolytic production of various compounds in the Mars northern polar region was developed. Galactic cosmic rays are used as the source of particle radiation. Particle energy distributions are modeled semi-empirically with the energy deposition inside the ice layers computed using the Stopping and Ranging of Ions in Matter (SRIM) model simulation or a customized Bethe-Bloch formula. The rate of species production is derived from laboratory measurement. Seasonal variations of the ice layers are either obtained from Global Multiscale Mars Model (GM3) results or estimation based on observed quantities. Preliminary results show that for species such as carbon monoxide, as much as 9,000 tons can be released into the atmosphere annually. Without the use of atmospheric transport models, a direct comparison to observations is not possible. As radiolysis can potentially explain the existence of compounds such as methane on Mars, the model warrants further investigation.
Open Access
Disc Winds and Line-Width Distributions in Active Galactic Nuclei
(2016-09-20) Chajet, Laura Susana; Hall, Patrick B
We study Active Galactic Nucleus (AGN) emission-line profiles by combining an improved version of the accretion disc-wind model of Murray & Chiang with the magnetohydrodynamic model of Emmering et al. We consider central objects with different masses and/or luminosities. We show how the shape, broadening and shift of the C IV line depend not only on the viewing angle to the object but also on the wind launching angle, especially for small launching angles. We have compared the dispersions in our model C IV line-width distributions to observational upper limits on that dispersion, considering both smooth and clumpy torus models. Following Fine et al., we transform that scatter in the profile line-widths into a constraint on the torus geometry. We show how the half-opening angle of the obscuring structure depends on the mass and luminosity of the central object.
Open Access
Monitoring Broad Absorption-Line Quasar Variability
(2016-09-20) Rogerson, Jesse Aaron; Hall, Patrick B.
Winds generated by an accreting super massive black hole may provide feedback to the host galaxy and offer an explanation for the co-evolution of galaxies with their super massive black holes that has been reported in the literature. Some outflows are manifested as broad absorption line (BAL) troughs in quasar spectra, and are measured at velocities as high as 60, 000 km s 1 at ultra-violet wavelengths. These BAL troughs have been observed to vary on both long (years) and short (weeks) rest-frame time-scales and can emerge in a quasar that had none, or disappear completely. By monitoring the variability of absorption in BAL quasars, constraints can be placed on outflow models and the structure of quasars in general. In this study, we isolate a set of quasars that exhibit emergent C iv BALs in their spectra, by comparing archival data in the SDSS Data Release 7 to the BOSS Data Release 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. BALs were formally detected in all but two of the quasars in the dataset, and we report 219 absorption complexes in the entire set. After a BAL has emerged, we find it is equally likely to continue increasing as it is to start decreasing in a subsequent observation. Based on the range of time between our observations, this indicates the coherence time-scale of BALs is less than 100 days. There is a strong signal of coordinated variability among two troughs in the same quasar. Further, coordination is stronger if the velocity separation between the two troughs is smaller. We conclude the variability is likely due to changes in the ionizing flux incident on the absorbing cloud, which agrees with the results of Filiz Ak et al. (2013). In this work we also test two competing models of BAL variability (bulk motion and ionization changes) in the context of a case study of the quasar SDSS J023011.28+005913.6, which had two high-velocity emergent troughs. Both models yield plausible results.
Open Access
The Impact of Atmospheric Models on the Dynamics of Space Tether Systems
(2016-09-20) Siewnarine, Vishal; Zhu, Zheng Hong (George)
Space debris has become an increasingly larger concern for aerospace travel and exploration. One idea to control the space debris population is to de-orbit defunct satellites using a space tether system. A space tether system is often made up of three parts: the main satellite, the tether and the sub-satellite. The tether connects the main satellite and the sub-satellite. Space tether systems make use of the Lorentz force as an electrodynamic drag for de-orbit. We use an established model of a space tether system to observe how satellites de-orbit. This model was constructed in MATLAB (Simulink) and uses the 1976 U.S. Standard Atmosphere. However, we wish to investigate how the model behaves using newer and more accurate atmospheric models, namely, the Jacchia-Bowman 2008 model and the Drag Temperature Model 2013. We also investigate the effect of controlling the tether's libration energy under the three aforementioned atmospheric models.
Open Access
Antihydrogen Via Two-Stage Charge Exchange
(2016-09-20) Fitzakerley, Daniel William; Hessels, Eric
This thesis describes positron and antihydrogen research performed at CERN in the context of the ATRAP collaboration. Positrons emitted from a radioactive source are moderated in a layer of frozen neon. The rate at which slow positrons exit the moderating material is precisely determined. The slow positrons are trapped in a differentially pumped Penning trap. Large numbers of positrons are accumulated and transferred into a cryogenic Penning trap at a record rate. Plasmas of up to four billion positrons are created --- the largest number of positrons ever held in a single trap. Counting techniques for positron and electron plasmas are compared, validating the charge-counting techniques used for each. Positron plasmas are compressed using rotating electric fields in preparation of antihydrogen production experiments. Antihydrogen atoms are created via laser-controlled, two-stage charge exchange. These antihydrogen atoms, approximately 2000 per trial, should be created with low enough energy so that some of them can be confined in a magnetic quadrupole or octupole trap. The goal of ATRAP is to precisely measure the spectroscopy of these trapped antihydrogen atoms, and compare it to the spectroscopy of hydrogen to test CPT and Lorentz invariance.
Open Access
Sensitivity Studies for Argus 1000 Micro-Spectrometer: Measurements of Atmospheric Total Column Carbon Dioxide By Reflected Sunlight
(2016-09-20) Alsalem, Naif Zaid M.; Quine, Brendan
A sensitivity analysis of the atmospheric boundary layer (ABL) and the atmospheric total column carbon dioxide was performed. The absorption of reflected solar radiation from the atmosphere and Earths surface near 1.58 m is utilized in this study. The CO_2 near infrared (NIR) bands at 1.58 m and 1.60 m are located within the Argus 1000 spectrometer spectral range, 1.0-1.7m. The model findings suggest that Argus 1000 spectrometer signal-to-noise ratio (SNR) must be 2000:1 to detect a 1% CO_2 change in the boundary layer (0-2 km). Argus 1000 spectrometer with its current SNR (~ 1520:1) can detect approximately 1.31% CO_2 change in the boundary layer (ABL). Two solar radiance paths were considered using GENSPECT, a line-by-line radiative transfer model, to examine the solar radiance spectra seen by the sensor. In path one, sunlight is assumed to travel through a longer path length in the atmosphere and reflect off the ground back to space. In path two, the solar beam is assumed to travel through a shorter path length and reflect off a cloud layer that is 4 km above the ground. The model findings suggest that the ratio between the solar radiances in both paths is approximately 4.5. The radiance change in both paths was examined for a 1% CO_2 perturbation in the boundary layer. The effect of the presence of clouds on both solar radiation and CO_2 absorption is also analyzed using flight data collected by the Argus 1000 spectrometer over cloudy and cloud-free scenes. The finding shows that CO_2 absorption in a clear sky condition is approximately 5.3% higher than when clouds are present.